6/20/2006 Case 1: Hemangiopericytoma encompassing meningioma

Clinical History:

Diagnostic Notes:

This was an H&E stained slide of a right
frontal mass from a 37 year old man, thought pre-operatively to most likely be
a meningioma. There was no significant medical history or familial history.
The mass was a neoplasm of mostly moderate to high cellularity, attached to
dura. The majority of the mass was a spindle cell lesion with rather small
cells which was moderately vascular. The cells were not whorled nor were they
arranged in lobules, and the pattern was that of a fairly cellular variant of
hemangiopericytoma and similar tumors, although staghorn vessels were not
obvious. In addition there was a nodule of lower cell density which was pale
on the H&E stain, and which had cells with a different character with a more
epithelioid appearance and a suggestion of some poorly-formed whorls. This
resembled a meningioma, and was wholly surrounded by the larger mass. Mitotic
figures could be found in the large mass but not in the small pale nodule
embedded in the larger mass.

Special stains showed that the main portion of the mass had some reticulin
around individual cells, mostly close to vessels, whereas the paler nodule had
none at all except around vessels themselves. The cells in the small pale
nodule were strongly vimentin and EMA immunopositive, whereas those in the
larger mass were mostly negative for both of these markers. A trichrome stain
showed extensive collagen deposition in the larger mass but not much in the
small nodule. A CD34 stain was negative in tumor cells in both parts of the
tumor, but did mark endothelial cells appropriately throughout the section. A
MIB1 stain showed a proliferation index of about 10% in the main portion of
the tumor but a much lower level in the small pale nodule.

The case was signed out by Dr Wolfe as a Hemangiopericytoma encomassing a
Meningioma. The membership generally agreed; there was some discussion about
arachnoidal cell hyperplasia in reaction to a hemangiopericytoma but most felt
that the nodule embedded in the larger mass was too large and not sufficiently
like an arachnoid granulation to be just reactive. There was also the usual
discussion of the differential diagnosis of hemangiopericytoma in the cranial
cavity and elsewhere, including synovial sarcoma in other body sites based in
part on typical chromosomal translocations, and solitary fibrous tumor. As
noted, however, the consensus agreed with Dr Wolfe's original diagnosis.